The closest thing I have to regrets is selling the more valuable stuff in my collection right before my kid was born. I sold a substantial chunk of my collection but specifically I miss, Star Fox Weekend, NTF2 Test Cart, Little Samson, Pocky and Rocky 1 & 2, and Dragon Fighter. We had a small emergency and really needed money quickly at the time. Selling those games helped us out without going into debt and we're better off for it.
I like to think I'll eventually get copies of those games someday but we just bought a house and that will suck up all my money for the time being